Grease is used for lubricating a gear, a bearing and the like in order to prevent friction to improve a driving efficiency and mechanical life thereof. However, in a field requiring a clean environment such as a clean room, precision machine production, semiconductor production, flat display production and food manufacturing, fine particles (for instance, an average diameter of 5 μm or less) that are generated from grease influences a production yield (hereinafter, generation of dust from grease is referred to as “dust generation”). Accordingly, such dust generation needs to be suppressed as much as possible.
Accordingly, for such an application, a so-called “low dust-generation grease,” which suppresses dust generation, has been proposed. For instance, there has been proposed a grease composition containing 10 to 35 mass % of a lithium stearate soap as a thickener and 0.5 to 15.0 mass % of one or more compositions selected from the group consisting of oxidized paraffin and diphenyl hydrogen phosphite (see Patent Document 1). Moreover, there has been proposed another grease composition containing 15 to 30 mass % relative to a whole composition of a lithium salt of a hydroxyl-free fatty acid having 10 or more carbon atoms, the lithium salt being formed in a fiber shape with a length and a diameter of 2 μm or less respectively (see Patent Document 2).